In WLAN (Wireless Local Area Networks), since an STA (Station, station) is usually battery-powered, and energy is limited, according to MAC (Medium Access Control, medium access control) layer specification defined by IEEE802.11, an AP (Access Point, access point) periodically broadcasts a Beacon (beacon) in accordance with a BI (Beacon Interval), and the STA working in a power saving mode periodically is awakened and receives the beacon, wherein the beacon is a management frame used for notifying the STA of certain specific information, the beacon contains a data structure TIM (Traffic Indication Map, traffic indication map) used for notifying the STA whether the AP caches a data frame belonging to the STA; the TIM itself is a virtual bit mapping table composed of 2008 bits, each bit in the TIM corresponds to a specific STA, and a status of each bit represents whether the AP caches data of a STA corresponding to the bit.
A current 802.11ah application scenario contains an intelligent meter reading scenario supporting up to 6000 STAs. When a large number of STAs are awakened, a PS-Poll (power saving-polling) frame needs to be transmitted to acquire downlink data. The PS-Poll is a control frame transmitted by an STA and is used for acquiring data cached in an AP from the AP; and competition induced by a large number of PS-Polls leads to additional energy consumption on the STA with a low energy consumption requirement. Moreover, an Offloading STA and a Sensor STA coexist in the network, and the Sensor STA may become a hidden node of the Offloading STA due to such reasons as small transmission power and the like, so that the Sensor STA with the low energy consumption requirement is more likely to generate collision with the Offloading STA, resulting in multiple retransmissions which generate additional energy consumption.
To solve the above problems, a competition method based on time slots is provided in the prior art, and this method combines access based on time-slot division, with CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) and requires each STA to begin to compete for a channel in a time slot to which it belongs. In addition, a competition for transmission of a PS-Poll is distinguished from transmission of downlink data by an AP, and they are divided into different time periods separately: the STA competes for a PS-Poll in a specified time slot within a specific time period, and the AP transmits data in a specified time slot within another time period after the specific time period according to a sequence of receiving PS-Polls. Therefore, the PS-Polls are scattered and are transmitted separate from the downlink data, thereby reducing the conflict probability of the PS-Polls, moreover, the STA successfully competing for the channel may shift to sleep and is not awakened until the AP is about to send downlink data to it, thus reducing the waiting energy consumption.
Although the existing technical solution provides a scattered PS-Poll competition method, an appropriate handling mechanism is unavailable when the STA can not successfully receive the downlink data within the divided time period; and in addition, the existing algorithm can not handle the problem of data packet retransmission when transmission of uplink data based on time-slot division is unsuccessful. Therefore, when the PS-Poll is lost or goes wrong, an acknowledgement frame ACK of the PS-Poll is lost or goes wrong or DATA transmitted by the AP is lost or goes wrong, the SAT can not correctly acquire downlink data or send uplink data.